The cooler bags we use nowadays have fixed liners. When liquid food or soup spills in the bag, the stitched seams of the liner are not waterproof and allow the liquid to soak all layers of the bag and in the meantime the water-impermeable liner material prevents thorough cleaning of the bag. The nutrient from the soup is absorbed by the spongy insulation layer, which creates a favorable medium for bacterial growth. In fact many people carry dirty-looking cooler bags with their lunch and supper in it.
As a cooler bag with fixed liner can't be cleaned, it will be discarded when it is dirty enough. So, it is considered a disposable item. As a disposable item, it is made with low-quality materials and craftsmanship.
I have designed a bag with a detachable liner. With the liner attached, it is a cooler bag. With liner detached, it is used as a usual carry bag. Such a bag with dual function of a cooler bag and a carry bag requires that the liner is waterproof without stitched seams to minimize the spoilage by spilled liquid food. In case of an extensive soup spill in the bag, the liner can be detached and the bag can be thoroughly cleaned and reused. A damaged liner can be easily replaced with a new one. A bag with dual function of cooler/carry bag can be expected to be a durable item instead of a disposable one and merits fine materials and craftsmanship and diverse design styles.
There are prior arts about removable bag liners, but they did not address the proper placement of the liner. The liner is either left outside the bag, which can be hard to find or be lost, or inside the bag, in which case the liner is exposed to the tear and wear by the items in the bag and also contributes to the mess in the bag.